The invention relates to the field of medical devices, and more particularly to an apparatus and method for measuring the distance between the operative distal end of a myocardial revascularization device and the endocardial and epicardial surfaces of the heart wall of a patient.
In the treatment of cardiovascular disease, transmyocardial revascularization (TMR) is a well known technique in which channels are formed in a patient's heart wall to supply blood flow to the ischemic heart tissue and to treat angina. The channels extend through the heart wall muscular surface, or myocardium, located between the epicardium and endocardium of the heart wall. In laser transmyocardial revascularization (LMR), a laser is used to form one or more channels in a patient's heart wall defining the heart chamber. The laser energy is typically transmitted from the laser to the heart tissue by an optical fiber, with a lens on the distal end of the optical fiber operatively engaging the heart tissue to be revascularized. Other energy systems, such as electrodes, may be used for myocardial revascularization.
Initial revascularization procedures required the chest wall to be opened for insertion of the revascularization device and penetration of the entire heart wall to form a channel through the myocardium into the endocardium. Copending application, Ser. No. 08/368,409, filed on Dec. 30, 1994 which is incorporated herein in its entirety, describes an intravascular system for percutaneous transmyocardial revascularization (PTMR) which eliminates the need of the prior procedures for opening the chest cavity and penetrating the entire heart wall. The PTMR system is introduced into a peripheral artery and advanced through the patient's arterial system into the left ventricle of the patient's heart, from where the revascularization channels are formed through the endocardium and into the myocardium.
Transmyocardial revascularization requires accurate measurement of the thickness of the patient's heart wall, in order for the procedure to be performed with maximum safety and effectiveness. Establishing the thickness of the heart wall at the location where TMR energy is to be discharged decreases the likelihood of injury to the patient from transmural perforation, and allows the physician to precisely control the channel formation by controlling of the depth of penetration of the discharged energy. TMR also requires establishing the distance between the operative distal end of a TMR device and the heart wall surface to determine when activation of the TMR device will effectively form channels within the patient's heart wall. Intimate contact between the operative distal end of the TMR device and the patient's heart tissue is necessary to provide sufficient transmission of the channel forming energy to the heart wall. Ranging information regarding the TMR device is therefore necessary to determine when contact between the TMR device and the heart wall surface has been achieved.
One of the difficulties with currently used PTMR devices has been the inability to accurate measurement of the thickness of the patient's heart wall at the precise location where TMR channels are to be formed. Information regarding wall thickness is currently obtained through echocardiographic analysis that may be performed either before or during the TMR procedure. However, methods of measuring heart wall thickness, such as transthoracic or transesophogeal echocardiography, only provide information for a small sample of locations on the heart wall and do not provide information regarding the precise location in which the TMR channels are to be formed.
Current methods used in TMR for determining contact with the heart wall have proven inadequate. In typical TMR devises, the physician determines the point at which the operative distal end has contacted the endocardium by observation of a fluoroscopic image of the optical assembly. However, fluoroscopic imaging requires a substantial amount of fluoroscopy time, and therefore exposes the patient to a large amount of radiation. Alternatively, the physician may infer contact from the observation of ectopic beats on the electrocardiogram, or from the observation of a reciprocating motion in the PTMR device produced when the device is in contact with the endocardial surface. However, these methods increase the expertise required to perform the procedure, and often provide ambiguous information.
What has been needed is the ability to reliably measure the thickness of the heart wall to be revascularized, and the distance between the operative distal tip of a PTMR device and the heart wall surface, in order to precisely control the channels formed in the patient's heart wall during PTMR. The invention satisfies these and other needs.